Captive Birth of Tiger Shark (Galeocerdo cuvier) Reveals a Shift in Respiratory Mode during Parturition
Ram ventilation, which is characterized by the production of a respiratory water current over the gill by locomotory effort, widely occurs among pelagic sharks. However, the process by which the juvenile starts this respiratory mechanism remains largely unknown. The captive birth of a Tiger Shark (Galeocerdo cuvier) at the Okinawa Churaumi Aquarium on 23 March 2017 permitted the examination of the parturition process and behavior of newborn juveniles of this species. Sonographic examination of the pregnant female showed that, unlike adult Tiger Sharks, embryos used buccal pumping, revealing that Tiger Shark shifts its respiratory mechanism from buccal pumping to ram ventilation after birth. Our observation also showed that ram ventilation of the neonate was not continuous, and buccal pumping was also used when the neonate intermittently rested on the bottom of the tank. We speculate that this behavior is the transitional phase in the shift from buccal pumping to ram ventilation in neonates, and continuous ram ventilation may be established after the development of continuous and fast swimming abilities.
Captive birth of a Tiger Shark at the Okinawa Churaumi Aquarium. (A) Photograph of captive pregnant female taken on 12 March 2017. (B) A part of the egg capsule (ec) is protruded from maternal cloaca. (C–F) Serial images of parturition behavior. A female quickly turned (0 to 4.9 s, C, D), egg capsule (ec) was excreted (7.4 s, E), and neonate (nn) was separated from maternal body (11.1 s, F). (G–J) Serial images of parturition process of a neonate. Posterior part of the neonate (arrow) was visible from outside of cloaca (G, H), and neonate was separated from maternal body (I, J).
Sonographic examination to determine the buccal pumping of the embryonic Tiger Shark. (A) Line drawings of the embryo showing the arrangement of embryo in sonogram. (B) Still image taken from sonographic video footage showing the locations of upper (a) and lower jaw (a') used for kinematic analysis. Upper jaw is shown in red and lower jaw in blue. (C) Opening and closing movement of an embryonic mouth (the y-axis indicates the distance between a and a' in panel B).
Sonographic examination to determine the buccal pumping of the newborn Tiger Shark. (A) Line drawings of the newborn juvenile showing the arrangement of newborn juvenile in sonogram. (B) Still image taken from sonographic video footage showing the locations of upper (b) and lower jaw (b') used for kinematic analysis. (C) Opening and closing mouth-movement of newborn Tiger Shark (the y-axis indicates the distance between b and b' in panel B).
Neonates “resting” on the bottom of the tank.
Contributor Notes
Associate Editor: D. Buth.